Weather Forecast


HORTISCOPE: Cut back lilacs, spade roots to get bushier shrubs

Driving a straightedge spade around the outer spread of lilacs to sever the roots usually will stimulate the plant into setting more flower buds. (Sarah Smith / Enterprise)

Q: I have some lilacs that bloom every year. They are very tall and planted in a row. For the most part, they only bloom on top. I have seen so many lilac bushes that are round and full and covered in blooms. How can I get mine to bloom like that?

A: After they finish blooming this year, cut them back before new growth begins. At the same time, take a straightedge spade and drive it into the ground around the outer spread of the lilacs to sever some of the roots. This usually stimulates the plants into setting more flower buds for the next growing season.

Q: I have a question about getting rid of a cotoneaster hedge. What is the best way to kill it? It was cut to the ground about two years ago but is growing again. I have evergreen trees about 20 feet away from this hedge, so will it hurt the trees if I use a herbicide? Do you have any other suggestions on how to get rid of it?

A: You can spray it with glyphosate when it leafs out. If you don't have any spray drift, your evergreens will be OK. Another approach is to let it come into full leaf this spring and then cut it down with a chain saw. Nail anything green that shows with glyphosate after that and you should be free of the hedge!

Q: We have a 10-year-old mock orange plant that we prune every year in the fall. We have pruned it early, too. Will we ever get flowers? We have had a few flowers down low on occasion. Do we have to stop pruning it to get a nice set of blossoms?

A: You should prune it immediately after flowering to have blooms the following year. Also, remove the oldest canes every three or so years. Cut it back to the base of the plant and get rid of the twiggy inside wood by cutting back to a crotch. Never cut back the ends of branches or else an ugly broom-shaped shrub will be the result.

Q: I was wondering if I could cut a large root on my red maple that is growing on top of my lawn. It makes it difficult to mow. Will cutting the root harm the tree?

A: Cutting a single root out of an otherwise healthy, mature red maple will not harm the stability or vigor of the tree.

Q: If a person were to apply a grub control product to control nightcrawlers, when is the best time to do that?

A: Right now. It takes time to work into the soil, so the sooner the better.

To contact Ron Smith for answers to your questions, write to Ron Smith, NDSU Department of Plant Sciences, Dept. 7670, Box 6050, Fargo, ND 58108-6050 or e-mail